<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .parent{
            border: 2px solid #333;
            width: 100px;
            height: 100px;
            box-sizing: border-box;
            /* 1.使用弹性盒实现 */
            /* display: flex;
            align-items: center; */

            /* 2.使用定位 */
            /* position: relative; */

            
           

        }
        .test{
            width: 40px;
            height: 40px;
            background-color: pink;
            /* position: absolute;
            top: 50%;
            left: 0;
            transform: translate(0, -50%); */

            /* 3.使用外边距 */
            /* margin-top:50%;
            transform: translate(0, -50%);  */
        }
    </style>
</head>
<body>
    <div class="parent">
        <div class="test"></div>
    </div>
</body>
</html>